Students calculate future sea-level rise in Olympia

Many scientists are working to establish what we can know about future climate. One statistician is focusing on what we can’t know – gauging the uncertainties around projections of climate change.

That professor helped eight University of Washington students do a detailed study of the rising level of south Puget Sound in Olympia, the state capital, and the uncertainties around those estimates. All are co-authors on a paper to be published in the Journal of Applied Meteorology and Climatology.

“As an educational experience, the class was pretty phenomenal,” said Peter Guttorp, a UW professor of statistics. “We expected it to take three or four weeks, but it took about eight weeks.”

Olympia’s downtown lies close to sea level. It was one of the first U.S. cities to look at effects of sea-level rise.

Students in the spring 2013 Statistical Climatology course did a case study on Olympia shorelines. They used the latest climate models to forecast global ocean temperatures and sea-level rise, then used historical records to relate those changes to sea level in Seattle. Finally they used a more limited set of tide gauge data to relate Seattle and Olympia high-tide marks.

The group found that by 2100 the water near Olympia will rise by 14 to 32 inches, or slightly more than the open oceans. Seattle water lines will rise by about the same amount, supporting the latest reports from the Intergovernmental Panel on Climate Change.

The undergraduate and graduate students – majoring in statistics, public policy and forestry – also used methods Guttorp developed to calculate the range around those estimates. Most of the uncertainty, they found, is in the global climate models.

Besides publishing a research paper, the students created a website and map to display their findings, as well as describe the scientific reasons for sea-level rise and outline policy options. Their interactive map includes the location of existing underground storage tanks, obtained from a City of Olympia website, which could pose a hazard if the groundwater rises to that level.

“I really liked the collaborative atmosphere,” said student Harry Podschwit. The class would meet for discussions twice a week and then work to look up information, run calculations or write computer programs. “I learned a lot about policy, and that was important for developing a foundation of a scientific career.” He is now a graduate student in the UW’s interdisciplinary program in Quantitative Ecology and Resource Management.

The City of Olympia has been planning for sea-level rise since 1990. The city’s low-lying downtown and location at the tip of Puget Sound made it one of the first in the country to look at this issue. Even if the sea was motionless the high-water mark would depend on the topography. But water also sloshes around with weather and the tides, and Budd Inlet, at the very tip of Puget Sound, can already see a tidal range of 22 feet.

The new research paper includes graphs of the projected sea-level rise in Olympia during this century. The authors also flip the question around, looking at when the sea could reach some key points.

“It might be useful to know how likely is it to get a certain level by some date?” Guttorp said. “It’s difficult to get those error bars.”

For example, the study shows that water is likely to rise 10 inches by around 2050, but there’s a 90 percent chance the water will cross that 10-inch mark sometime between 2029 and 2075.

Guttorp studies how uncertainty changes when moving from global climate models down to the regional models needed to create policy on such things as whether to build retaining walls, when to revise building codes and where to relocate crucial infrastructure.

The group shared its website with Olympia City Council and hopes the results can support local planning efforts. The paper also addresses broader questions about how to account for uncertainty in projections of sea-level rise.

The other UW student authors are Alex Januzzi, Marie Novak, Lee Richardson, Colin Sowder and Aaron Zimmerman. Other co-authors are David Bolin and Aila Sӓrkkӓ at Gothenburg University in Sweden. All are also co-authors on a second, more technical, paper to be published in Statistica Sinica.

The research was funded by the National Science Foundation and Sweden’s Knut and Alice Wallenberg Foundation.